TAMR is expected to be one of the future generations of magnetic recording technologies that will enable recording at ˜1-10 Tb/in2 data densities. TAMR involves raising the temperature of a small region of the magnetic medium to near its Curie temperature where both of its coercivity and anisotropy are significantly reduced and magnetic writing becomes easier to achieve even with weak write fields characteristic of small write heads in high recording density schemes. In TAMR, optical power from a light source is converted into localized heating in a recording medium during a write process to temporarily reduce the field needed to switch the magnetizations of the medium grains. Thus, with a sharp temperature gradient of TAMR acting alone or in alignment with a high magnetic field gradient, data storage density can be further improved with respect to current state of the art recording technology.
In addition to the components of conventional write heads, a TAMR head also includes an optical waveguide (WG) and a plasmon generator (PG). The waveguide serves as an intermediate path to guide laser light from a source to the PG where the light optical mode couples to the propagating plasmon mode of the PG. After the optical energy is transformed to plasmon energy with energy transmission along the PG, it is concentrated at the medium location where heating is desired. ideally, the heating spot is correctly aligned with the magnetic field from the write head to realize optimum TAMR performance.
As increased recording density is required in hard disk drives (HDD), thin-film magnetic heads must deliver improved performance. Thin-film heads with a composite structure in which a magnetoresistive (MR) sensor device is laminated with a magnetic recording device are widely used. These two devices read and write data signals, respectively, from and onto magnetic disks that are magnetic recording media.
A magnetic recording medium may be considered a discontinuous body wherein magnetic fine particles are assembled. One recording bit comprises a plurality of magnetic fine particles each having a single domain structure. Therefore, in order to enhance recording density, it is necessary to shrink magnetic fine particle size thereby reducing irregularities at boundaries of recording bits. However, a decreased volume that is associated with smaller magnetic fine particle size tends to cause a deterioration of thermal stability in magnetization which is a problem.
An index of thermal stability in magnetization is related to KUV/kBT where KU is the magnetic anisotropy energy of a magnetic fine particle, V is the volume of one magnetic fine particle, kB is the Boltzmann constant, and T is the absolute temperature. A smaller magnetic fine particle size only reduces V which lowers KUV/kBT and worsens thermal stability. Although KU may be increased to counteract this problem, a larger KU increases the coercivity of the magnetic recording medium. One must consider that the writing magnetic field intensity caused by a magnetic head is substantially determined by the saturated magnetic flux density of a soft magnetic material constituting a magnetic pole within the head. As a result, no writing is accomplished if the coercivity exceeds a permissible value determined by the limit of writing magnetic field intensity.
A solution to the aforementioned thermal stability problem is needed in a TAMR scheme where heat is applied to a magnetic recording medium immediately before applying a writing magnetic field while using a magnetic material having a large KU value so as to enable writing with lowered coercivity. The TAMR scheme is roughly classified into magnetic dominant recording and optical dominant recording. In magnetic dominant recording, writing is attributed to an electromagnetic coil component while the radiation diameter of light is greater than the recording width. In contrast, for optical dominant recording, writing is attributed to a light-radiating part while the radiation diameter of light is substantially the same as the track width (recording width). Thus, magnetic dominant recording and optical dominant recording impart space resolution to a magnetic field and light, respectively.
In a TAMR recording device, light is emitted from a source such as a semiconductor laser into an optical waveguide that is surrounded by a cladding material. Light is focused by the plasmon generator at the end of the waveguide to heat the surface of the magnetic medium. Since the focused light power is intense, temperatures may reach 450° C. in the vicinity of the PG and cause reliability issues with PG structures made of Au that is typically employed because of its high thermal transmission property and high plasmon propagation efficiency. A new TAMR recording head design is needed, especially in the vicinity of the PG, to substantially increase thermal stability of the PG and adjacent components, and thereby improve device reliability at elevated temperatures.